[PATCH] D120600: [ELF][X86] Don't create IBT .plt if there is no PLT entry

[Fangrui Song via Phabricator via llvm-commits]

MaskRay updated this revision to Diff 411566.
MaskRay retitled this revision from "[X86][LLD] Fix PLT emission by LLD when -fcf-protection=branch is used" to "[ELF][X86] Don't create IBT .plt if there is no PLT entry".
MaskRay edited the summary of this revision.
MaskRay added a comment.

Fix description and add tests


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D120600/new/

https://reviews.llvm.org/D120600

Files:
  lld/ELF/SyntheticSections.cpp
  lld/ELF/SyntheticSections.h
  lld/test/ELF/x86-64-feature-cet.s


Index: lld/test/ELF/x86-64-feature-cet.s
===================================================================
--- lld/test/ELF/x86-64-feature-cet.s
+++ lld/test/ELF/x86-64-feature-cet.s
@@ -91,6 +91,17 @@
 # DISASM-NEXT:               jmpq    *0x2126(%rip)
 # DISASM-NEXT:               nopw    (%rax,%rax)
 
+## If there is no PLT entry, don't create .plt section.
+# RUN: ld.lld -e 0 %t1.o -o %t.noplt
+# RUN: llvm-readelf -S %t.noplt | FileCheck %s --check-prefix=NOPLT
+# RUN: ld.lld -r %t1.o -o %t.noplt
+# RUN: llvm-readelf -S %t.noplt | FileCheck %s --check-prefix=NOPLT
+
+# NOPLT:     [Nr] Name
+# NOPLT-NOT: .plt
+# NOPLT:     .note.gnu.property
+# NOPLT-NOT: .plt
+
 .section ".note.gnu.property", "a"
 .long 4
 .long 0x10
Index: lld/ELF/SyntheticSections.h
===================================================================
--- lld/ELF/SyntheticSections.h
+++ lld/ELF/SyntheticSections.h
@@ -761,6 +761,7 @@
 public:
   IBTPltSection();
   void writeTo(uint8_t *Buf) override;
+  bool isNeeded() const override;
   size_t getSize() const override;
 };
 
Index: lld/ELF/SyntheticSections.cpp
===================================================================
--- lld/ELF/SyntheticSections.cpp
+++ lld/ELF/SyntheticSections.cpp
@@ -2696,6 +2696,8 @@
   return 16 + in.plt->getNumEntries() * target->pltEntrySize;
 }
 
+bool IBTPltSection::isNeeded() const { return in.plt->getNumEntries() > 0; }
+
 // The string hash function for .gdb_index.
 static uint32_t computeGdbHash(StringRef s) {
   uint32_t h = 0;


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